Crystal rectifier tube



July 12, 1960 D. A. LANCIANI 2,945,122

CRYSTAL RECTIFIER TUBE Filed Oct. 11, 1955 INVE DANIEL A. LA .Nl

BY Ha n37, i /w I I, I

ATTORNEYS CRYSTAL RECTIFIER TUBE Daniel A. Lanciani, West Medford, Mass,assignor to Microwave Associates, Inc., Boston, Mass a corporation ofMassachusetts Filed on. 1-1, 1955, Ser. No. 539,786 *6 Claims. 01.250-41 The subject invention relates to a mixer crystal rectifier tubeand particularly to a rectifier crystal tube for coupling a rectangularwave guide to a rectifier crystal in the millimeter Wave length region.

Mixer crystal rectifiers designed for thelower microwave frequencies andof a convenient size and shape have been constructed for use with bothcoaxial and wave guide mounting arrangements. As the Wave lengthdecreases below one centimeter, however, it has been found impracticalto scale down the traditional coaxial designs. for example, the 1N53type of crystal coaxial cartridge for l centimeter use is limited to aninner diameter of .045 inch and an outer conductor diameter of .125 inchin order that the cut-olfwave length of the next higher mode (TE11) inthe coaxial section would be substantially less than on the lowestanticipated operating wave length. This provided a resulting cut-offwave length for the cartridge of .635 centimeter which was well belowthe expected operating range for that design.

However, application of the same considerations in the 4 millimeterregion results in inner and outer conductor diameter of .023 inch and.063 inch respectively. These dimensions are obviously too small to bepractical. It has therefore proved necessary to design new types of waveguide mounted crystals for rectifier use in the millimeter region. Onesuch device'has been suggested by Dr. G. C. Southworth in-his book,Principles and Applications of Wave Guide Transmission, Van NostrandCo., New York, 1950 on page 653 (chapter 12). In this design the crystalis mountedin a cylindrical metal housing or cartridge which couples tothe rectangular guide through a hole in the side of the cylindricalhousing. An adjustable plunger on one side of the cavity in thecylindrical housing carries the crystal and a whisker projects acrossthe opening to the crystal.

It is the object of this invention to provide an improved and moreeasily manufactured millimeter rectifier tube of convenient size and aconstruction which may be readily assembled. V

It is a feature of this invention that it utilizes a hollow metalliccylinder or cartridge to house the rectifier, said cartridge beingadapted to propagate the TE-ll mode of round wave guide, together withan inner circular to coaxial transition assembly which feeds energy tothe whisker silicon junction. 7 A further feature of this invention isthe use of a dielectric end seal adjacent the rectangular wave guide towhich this assembly is mounted. This dielectric seal functions as amatching transformer between the rectangular guide and the cartridgewhereby the position of the remaining RF portions of the rectifier arerendered more or less independent of their distance from the junction.It is a still further feature of this invention that it providesimproved and simplified means for RF choking and capacitive bypassing ofthe IF output lead.

erence to the following figures:

Fig. 1 illustrates a cut-away elevation of the entire rectifier tubeassembly.

Fig. 2 is a cross-section through the case and retaining shell showingthe poistioning key.

Fig. 3 shows the dominant TEIO mode configuration in a rectangular waveguide.

Fig. 4 shows the dominant TEll mode in a circular wave guide.

Fig. 5 shows the electric field configuration in the vicinity of theconverting fin.

As illustrated by reference to Figs. 1 and 2 this invent-ion utilizes acylindrical case or cartridge 10 appropriately mounted to an opening 11in a rectangular wave guide section 12 As illustrated the cartridge ismounted coaxially with the rectangular guide but it would also beappropriate to mount the device on the side of a rectangular sectionhaving a tuning end plunger. For convenience the case 110 is held by acylindrical shell 13 having an end flange 15 which is fastened to theend flange of the rectangular guide. The other end of the shell carriesa bayonet structure 23 to matewith a standard BNC connector therebyjoining a coaxial line to the output end of the crystal tube. Thus thetube is a shielded separable insert which may be easily replaced a ifthe crystal should burn out. The bayonet connector tends to press thetube into firm contact with the waveguide end. The key 14 projectingfrom the inside of the shell .fits into the slot 17 in the case therebyaligning the case, including in particular the mode converting fin to bedescribed later, with respect tothe TElO mode in the rectangular guide.I

While direct coupling is shown between the endof the rectangular guideand the end of the case, a quarterwave choke coupling may under somecircumstances be desirable. The key and slot structure would tend tointerfere with the operation of such a choke joint if located near thecenter of the top or bottom of the rectangular guide. Therefore this'structure'may in some cases be located at the side where the electricfieldis at a minimum. To assure proper alignment of the shell and keythe pin 19 on the shell is fitted to the hole 21 in the I end flange ofthe rectangular guide.

The dielectric plug 16 is fitted to the end of the case or cartridge 10adjacent the junction with the rectangular wave guide 12. It is thefunction of this plug to act as a moisture-sealing window and at thesame time to serve as a junction matching device. If this dielectricplug were made to have an eifective length of one-half wave length, thewindow would be refiectioiiless within the circular wave guide portionof the case 10 adjacent the rectangular guard. However, the RF impedancemismatch created by the junction would then have'to be compensated withproper dimensioning of the remaining whisker silicon geometry. Thiswould have the critical disadvantage'of requiring these rectifyingelements to be precisely located a specified distance from the junctionand in addition the relatively large distance between the junctionreflection and the compensating reflection of the whisker would tend tomake the unit frequency sensithe TE-ll mode in the circular guide 10. VIn the 4 millimeter region this dimension should be accurate to within.001". In addition the plug element 16 is designed to have acharacteristic impedance which is the geometric mean between theimpedance of the rectangular wave T1118 invention will be more easilyunderstood by refguide 112 and the circular wave guide element orsection 10. Described mathematically where Z is the impedance of thefilled circular guide V 3 and Z and Z; the impedances of the air filledrectangular and circular guides respectively. The wave length ofdielectric filled circular guide may be closely approximatedbymultiplying the wave length in air filled circular guide where K isthe dielectric constant. For use inthe. millimeter wave region, it hasbeen found that Teflon having a dielectric constant of approximately2.15 is an ap-.

propriate material to lower the impedance of the circular- -To connectthe circular wave guide section to the silicon junction an additionaltransition element 18 in the form of a circular to coaxial transitionfin is utilized. This fin is mounted for ease of assembly in acylindrical conductive section 2%) which may be press-fitted into thecylindrical interior of case 10 to appropriately position the fin 18with respect to the plug 16. To provide a compact design, the fin ispositioned adjacent to the plug 16 and the conductive cylinder 20 isrotated in position about the axis of the tube 10 to appropriately alignfin 18 with respect to the TElO mode propagating in the rectangularguide 12. Since the cartridge is a separable unit the fin is actuallyoriented with respect to the aligning element 14 on the exterior of thecase 10 so that upon assembly with the rectangular wave guide the finwill be appropriately oriented.

slab having parallel sides, a front face sloping upward away from thefront of the cartridge at an angle of approximately with the axis andhaving a substantially vertical rear face in the same plane as the endof the cylindrical supporting section 20. The pure silicon wafer ismounted on a raised boss projecting on the order of ,52" from the rearface of the fin 18 on the axis of the tube 10. It has been found that acircular to ooaxial transition of this type is substantially moreefficient 7 11 from the silicondiode, particularly during assembly. h

This spacer is preferably of thin material to avoid interfering with thecoupling between the whisker and the cavity surrounding it. 'The spacermay be of metal .provided that it is not thick enough to short out theplunger 28 to the case 10.

4 of theinsulating material 26. The capacitance between the surface ofthe plunger and the inner wall of the case is designed to beapproximately seven microfarads for 4 millimeter operation.

The plunger 28 is cylindrical and has a cylindrical internally threadedopening 34. A metal pin preferably in the form of two sections 36 and 38are threaded to fit this opening. The threaded pin 36 carries on itsforward end the whisker 40 having a sharpened point which makes contactwith the silicon wafer. The whisker 4-0 has a bent center section in theform of a helical spring which prevents the pressure on the upper pointagainst the wafer to beadjusted without any tendency for the point toslide ofi its location on the axis of the case 10. The pressure of thiscontact is adjusted by rotating the pin 36 to screw it into the cavity34 the required distance. A slot 42 is provided in the back of this pinto facilitate this adjustment. When this adjustment has been made thesecond section of the pin 38 is screwed into the cavity and serves tolock the first pin in position. This second pin 38 projects backwardinto the rear section of the cylindrical housing pin to provide asuitable IF output connection.

In operation the above described millimeter wave rectifier operates asfollows. Microwave power propagating in the rectangular wave guide 12 inthe form of energy in the dominant TElO mode as illustrated in Fig. 3 isefiiciently transformed with the aid of the dielectric matching window16 into the TEll mode operating the forward part of the circularcartridge 10, as illustrated by reference to Fig. 4. This circular TEllmode is thereafter intensified in the center of the case by the couplingloop in the form of a triangular fin 18.

The electric field intensity and distribution is shown approximately inFig. 5. Coupling between the RF field and the junction is accomplishedin the cavity surr0unding the whisker. The intense field in the regionof the p f fin tends to bend parallel to the whisker after passing Thefin 18 is preferably in the form of a triangular away from thetransition fin. While the mode configuration is complex and the mode isnot purely coaxial in form it is similar to coaxial propagation and thefin may be convenientlydesignated asa circular to coaxial transitionfin. The propagation of RF power into the IF output section is blockedby theoperation of the flangechokingelement 28 which isformed as anintegral part of the IF output.

While the presently preferred embodiment utilizes the above-describedcoupling loop in which the silicon wafer is mounted to thetransition finand the whisker to the pin, it would he obviously possible to' reversethis arrangement and mount the whisker to the fin and the silicon' waferon the pin. Such an arrangement would in crease the'displacement of thesilicon from the trailing edge of the transition fin and thisdisplacement has already proven effective in improving performance atsome frequencies. The entire device may be easily assembled since all ofthe parts are in the form of cylindrical elements which may be fitted tothe inside of the cylindrical Adjacent and abutting this spacer is thecylindrical intween the front face of the first flanges and the inner.

cylindrical surface ofthe groove iseifectivelyone-half wave lehg'th;taking into account the dielectric constant case and the case 10 in turnis groovedto permit appropriate alignment of the fin 18 with respect tothe rectangular wave guide 12. a

While this invention has been described with respect to a singleembodiment it will be understood that the exact construction, of theinvention may be varied by those skilled in the art Without departingfrom the scope of this invention as described in the following claims.

I claim:

1. A crystal millimeter rectifier mounting device for use witharectangular waveguide comprising a cartridge having a cylindricalcentral opening adjacent the rectangular guideand in sequencethereafter, a cylindrical ,di electric sealing element matching thecircular wave guide impedanceto that-of the rectangular guide, acircular to coaxial tfansforming fin conductively mounted to saidcartridge, an axially mounted crystal-whisker assembly,

, one element of which is conductively mounted to said fin and the otherelement of which is electrically isolated from the cartridge, andconnecting means for the IF crystal output.

2. A crystal rectifier mounting comprising a rectangular wave guidehaving an opening, a sealed cylindrical case having a dielectric sealingwindow adjacentthe rectangular wave guide opening to establish acircular mode of propagation in the cylindrical case, a circular mode tocoaxial mode transition fin conductively mounted to said case adjacentthe dielectric window, a rectifying crystal mounted to the trailing edgeof said fin, a cylindrical insulating sleeve supported on said casefacing said trailing edge of the fin, a pin mounted in said sleeve, awhisker mounted on the forward end of said pin and in contact with thecrystal, and keying means for mounting the cylindrical case to therectangular guide whereby the fin is oriented with respect to thedominant mode in the rectangular guide.

. 3. A crystal wave guide rectifier cartridge for use with a rectangularwave guide having an aperture and propagating the TElO mode comprising acylindrical case having an open end in which the related circular TEllmode will propagate, means for mounting the open end of said case in theaperture, a sealing cylindrical dielectric plug in the case adjacent theaperture having an effective length of substantially one-fourth wavelength and having a characteristic impedance adapted to match theimpedance of the two wave guides, a circular to coaxial coupling loopconductively attached to said case and oriented parallel to thedominantelectrical mode in the cylindrical case, a silicon-whiskerassembly mounted along the axis of the case one element of which ismounted in the coupling loop and the other of which is mounted on aconductive pin displaced from said loop and insulated from the case.

4. A very high frequency crystal rectifier mounting for use withrectangular waveguides comprising a conductive circular case, meansadapted for mounting said circular case on a rectangular wave guide, adielectric sealing window adjacent the rectangular guide having acharacteristic impedance between that of the rectangular and circularguides whereby the end seal acts as a matching transformer, a circularto coaxial transformer fin of substantially triangular shape mounted inthe case parallel to the short sides of the rectangular guide and havinga forward face slanting backward from the side of the case and asubstantially vertical rear face, a crystal mounted on said rear face atthe axis of said circular case, an insulating sleeve supported on saidcase facing said rear face of said transformer fin, a conductive chokeelement mounted in said sleeve, a pin movably mounted in said choke foradjustment along the axis and projecting backward into the open end ofthe case to provide a coaxial output connector, and a whisker connectingthe end of said pin and the crystal.

5. A wave guide mounted rectifier cartridge comprising a cylindricalcase, a dielectric sealing impedance matching cylindrical plugeffectively one-fourth wave length long in the end of said case, asubstantially triangular circular to coaxial transforming finadjacentsaid dielectric plug, a rectifying crystal mounted to said fin,a cylindrical insulating sleeve supported on said case facing said finon the side opposite of said plug, a cylindrically conductive chokeelement mounted in said sleeve, a first pin threaded to said choke foradjustment along the axis of the case, a whisker on said pin in contactwith the crystal across a cavity to the rear of the fin and a second pinthreaded to said choke projecting backward into the open end of saidcase whereby rotation of the second pin will lock the first pin inposition.

6. A millimeter wave crystal rectifier for use with a rectangular waveguide having an opening comprising a circular cartridge having adiameter at least equal to the largest diagonal dimension of therectangular wave guide, means for mounting said cartridge over theopening in the rectangular wave guide, a moisture sealing transformercoupling dielectric window in the cartridge adjacent the rectangularwave guide having an effective length of approximately one quarter thewave length of the dominant mode in the dielectric filled cartridge andhaving an impedance characteristic approximating the geometric mean ofthe impedances of the rectangular wave guide and the circular cartridgewhereby the remaining RF portions of the rectifier mounting are renderedsubstantially independent of their distances from the junc tion betweenthe rectangular guide and the cartridge, a silicon rectifier element, acircular wave guide to coaxial wave guide transition element forcoupling microwave energy from the circular wave guide in the form of atriangular fin having parallel sides, a front edge slanting a move thewhisker along the axis, said choke section having appropriatelydimensional flanges, and a cylindrical dielectric sealing spacer toinsulate the choke and the pin from the cartridge wall.

References Cited in the file of this patent UNITED STATES PATENTS2,734,170 Engelmann et al. Feb. 7, 1956

